Function of lower esophageal sphincter will be studied in patients with reflux esophagitis in an effort to discover the cause(s) of sphincter failure which permits gastroesophageal reflux. Sphincter will be located by combining cineradiography with measures of mucosal potential difference and respiratory pressure reversal point. pH recordings will be used to measure reflux and this will be correlated with sphincter pressures measured at rest, during swallowing and stimulated by balloon distention. Sphincter function will be studied in the same patients after corrective surgery of varying types, correlating findings with clinical, cineradiographic and pH studies. Animal studies will be performed in an attempt to further elucidate anatomy and physiology of LES. In dogs (and later primates) squamo- columnar mucosal junction and hiatus marked with radio-opaque sutures. Cineradiography and pressure profile of LES performed simultaneously and findings correlated with microscopic anatomy. Role of GI hormones, particularly gastrin, on LES will be studied in chronic, surgically prepared dogs. In addition the role of pH in regulation of LES function will be studied.